WO2001098220A1

WO2001098220A1 - Briquette, method for its manufacture and its use

Info

Publication number: WO2001098220A1
Application number: PCT/FI2001/000579
Authority: WO
Inventors: Michael Perander; Jean Le Bell
Original assignee: Paroc Group Oy Ab
Priority date: 2000-06-20
Filing date: 2001-06-19
Publication date: 2001-12-27
Also published as: FI20001459A0; AU2001270648A1; FI110607B; FI20001459L

Abstract

The present invention is directed to a briquette, especially for mineral wool production, containing a particulate mineral material and a binder. The binder comprises an amorphous silicate based gel binder containing silica and alumina in a molar ratio in the range of 2 - 12. The invention is also directed to a method for making the briquettes, as well as to a method of mineral wool production, using the said briquettes as a raw material.

Description

BRIQUETTE, METHOD FOR ITS MANUFACTURE AND ITS USE

FIELD OF THE INVENTION

The present invention relates to a briquette containing particulate mineral material and a binder therefor. The invention also relates to a method for the manufacture of the briquette, as well as to its use, for example for mineral wool production.

BACKGROUND OF THE INVENTION

Many industrial processes use a mineral raw material charge in the form of briquettes, rather than in the form of natural materials as such. Especially when strict restrictions are to be put on the composition of the end product to be made from the briquette, the use of natural mineral materials is not always satisfactory as the composition of natural mineral materials vary to at least some degree. By using prefabricated mineral briquettes rather than natural materials it is thus possible to improve the control of the chemical composition of the charge. Another reason for using briquettes rather than natural materials is the possibility of optimizing the particle size of the starting material with respect to the particular industrial process contemplated.

Particle size of the charge is a problem especially in connection with mineral wool manufacture. Mineral wool is manufactured by melting mineral raw material in a melting furnace, either in a traditional cupola furnace, in a gas cupola furnace or an electrical furnace. In the different furnace types, heat energy is introduced in the mineral raw material in different ways: in a traditional cupola furnace the mineral raw material is charged together with the fuel, usually coke, in a gas cupola furnace heat is introduced by burning gas or some other fluid fuel, and in an electrical furnace electrodes are used which extend into the furnace.

One problem with cupola furnaces is that only relatively coarse material can be used as more finely ground material has a tendency to form a compact mass in the furnace, which makes the necessary flow of air and flue gases through the charge difficult. L addition, finely ground material is more difficult to handle and it gives rise to inconvenient dust formation, wherefore the use of finely ground material is problematic also in electrical furnaces. Consequently it is not possible to use all the raw material sources which otherwise would be available, for example the waste, that is excess fibres and unfiberized material, so called pearls or shots, which are produced during mineral wool manufacture, certain slag types, industrial waste from flotation processes, or for example the finest fractions from crushing of coarser material. This naturally means an economical loss, but also a limitation of available raw material compositions.

Attempts have been made at forming finer raw mineral material into briquettes. For this purpose it is known to use, as a binder in raw material briquettes, hydraulic binders, especially portland cement and clay as well as water glass (SE 205 247). The use of portland cement has the disadvantage that the briquette exhibits poor heat durability and looses its strength and turns brittle already at relatively low temperatures of 400 to 500 °C. The EP B 546 000 describes the use of a binder made from slag activated with an alkaline agent for use in a briquette for mineral wool production. Such slag has a glassy structure and is in a granulated form, which is easily activated with an alkaline agent. According to this patent, raw material briquettes are formed which exhibit good strength characteristics after manufacture, especially against moisture, and good performance in the melting process itself.

The present invention is aimed at providing a further improvement in the manufacture of briquettes containing particulate mineral material. In the context of the invention, the term briquette is to be interpreted as meaning various kinds of agglomerates, i. a. also pellets and granules. The briquettes according to the invention are especially suitable for mineral wool production, although also other briquette uses are conceivable, such as any use where the excellent binding properties of the binder can be taken advantage of. Such a use can be, for example, in iron ore briquettes for iron manufacture.

SUMMARY OF THE INVENTION

Accordingly, an object of the present invention is a briquette containing a particulate mineral material and a binder for the mineral material. According to the invention the binder comprises an amorphous silicate based gel binder having a content of silicium and aluminium, calculated as their respective oxides, that is of silica and alumina, wherein the molar ratio between silica and alumina (SiO₂/Al₂O₃) is in the range of 2 - 12, that is 2: 1 - 12: 1. Preferably the said range is 2.5 - 8, in particular 3.5 - 6.

The present invention is also directed to a method for the manufacture of briquettes containing a particulate mineral material and a binder, the method comprising the steps of

- providing a particulate mineral material,

- mixing the mineral material with the binder, and water, if necessary, - shaping the so formed mixture into briquettes, and

- hardening the so formed briquettes, whereby a binder is used which comprises a colloidal silicate dispersion containing silica and alumina in a molar ratio in the range of 2 - 12.

The invention is also directed to a method for the manufacture of mineral wool, whereby mineral raw material in the form of briquettes containing a particular mineral material and a binder, is added to a melting furnace, the formed melt is withdrawn and fiberized. The method is characterized in that the binder in the briquette comprises an amorphous silicate based gel binder containing silica and alumina in a molar ratio in the range of 2 - 12.

The briquettes according to invention show improved properties due to the increased alumina content in the binder. Such properties manifest themselves i.a. as improved strength and stability.

DETAILED DESCRIPTION OF THE INVENTION

The silicate based binder to be used in the briquettes according to the invention can be characterized as being an amorphous porous silica based gel, i. e. an aerogel, which is obtainable by dissolving a particulate silicate mineral material containing silica and alumina in a molar ratio of 2 - 12 in an aqueous solution to form a solution containing nucleated re-precipitated particles of the material, which solution is stabilized to form a colloidal dispersion and coagulating the dispersion to form a gel which, when dry, forms the desired amorphous gel.

The binder has excellent binding, strengthening and fire resistant properties and is also acceptable from a use or labour hygiene point of view. In addition, the binder can be manufactured from inexpensive and easily available raw materials, or by-products from industrial processes, in a simple manner, allowing for the tailor-making of or designing the composition of the binder to suit the desired purpose. An important advantage is that the binder for use according to the invention presents no ecological load on the environment, but contains only such components that are already inherently present in nature.

According to an advantageous embodiment of the invention, the binder used has, in contrast to traditional water glass, which has been used i.a. for the binding of briquettes for example for mineral wool production, a low alkali content, that is, it has a low content of alkali oxides, in particular sodium and potassium oxides. According to a further advantageous embodiment, the dispersion contains also earth alkali metal oxides, such as calcium and/or magnesium oxides. Such an embodiment gives i.a. improved water resistance properties to the briquette due to the fact that the aqueous solubility of earth alkali metals is inferior to that of, for example, the alkali metals.

According to an embodiment of the invention, the binder contains silica and alkali oxide in a molar ratio, that is the ratio of the silica moles to the sum of the alkali oxide moles, that is essentially the sum of the sodium oxide and/or potassium oxide moles, which is in the range of 10 - 350, preferably 15 - 150. The desired molar ratio can be obtained by properly selecting the starting mineral raw material to be used for making the binder dispersion.

According to a further embodiment of the invention, the binder contains calcium and/or magnesium oxide and/or iron oxide, wherein the molar ratio between silica and the sum of calcium oxide, magnesium oxide and iron oxide is in the range of 0.5 - 2, preferably 0.6 - 1.5. The iron oxide is calculated in the form of FeO

The binder to be used in the briquette according to the invention is obtainable by dissolving a particulate mineral material containing silica and alumina in a molar ratio of 2 to 12 in an aqueous solution, to form a solution containing nucleated re- precipitated particles of the material, stabilizing the so obtained solution to form a colloidal dispersion, i.e. a silicate containing sol, having a desired particle size, and op- tionally adjusting the dry matter content of the dispersion, and/or optionally coagulating the dispersion to form a gel.

According to a preferred embodiment, the primary particle size of the dispersion in the form of a sol is 1 to 1000 nm, preferably 10 to 100 nm.

The dry matter content of the dispersion used to form the binder can vary, depending on the intended application, but for most purposes a dry matter content, above 1 % by weight, such as ranging between 5 and 60 % by weight is suitable. The dry matter content of the dispersion can be adjusted by removing water, for example by evaporation, or adding water in a suitable manner.

As is explained in more detail below, the dispersion can easily be converted to a gel, for example using physico-chemical means, such as removing the electrostatic repulsion between the sol particles by changing pH or by adding an electrolyte, or a surfactant. Gel formation can also be carried out by drying the dispersion. As explained above, the colloidal binder dispersion can be used as such, whereby the binder can be converted to a gel, typically immediately before applying the same to the mineral materials to be bound, or is converted to a gel when in the end product, that is, in the briquette.

Preferably the particulate mineral material used as a starting material for making the binder is a material having a glassy amorphous structure. Such a glassy structure has better dissolution properties than a crystalline structure and is formed when mineral raw materials are molten and formed into fibres at high temperature. A suitable raw material is thus a mineral wool material or mineral fibre product, for example a waste or by-product from mineral fibre production, such as spinning waste, unused fibres or products, as well as post-consumer mineral fibre products. Naturally a material is chosen which has an optimal or desired composition for the preparation of the binder.

A mineral material suitable for use as a starting material contains SiO₂in an amount of 35 - 45 % by weight and Al₂O₃ in an amount of 8 - 25 % by weight.

According to an advantageous embodiment a low alkali particulate mineral material contains, calculated as % by weight, SiO₂ 35 - 45

Al₂O₃ 10 - 25

R₂O 0.2 - 3, wherein R means Na or K. In addition, such a material can contain, calculated as % by weight,

CaO 12 - 35

MgO 6 - 20

FeO (total iron) 2 - 10.

A further suitable mineral material is a material having the following composition, calculated as % by weight

SiO₂ 35 - 45

Al₂O₃ 8 - 13 R₂O 0.2 - 1, wherein R means Na or K. In addition, such a material can contain, calculated as % by weight, CaO 30 - 40

MgO 5 - 11

FeO (total iron) 0.1 - 1.

This composition is a typical composition for example for a slag wool product. Thus an advantageous starting material for making the dispersion can be a product or by-product obtained from the manufacture of slag wool.

The inclusion of earth alkali metal oxides has the further advantage of providing materials suitable for water resistant binders. Such inclusion is of special importance for example when used in briquettes, such as raw material briquettes for mineral wool production, or in ore briquettes.

Preferably the starting material used for forming the binder dispersion is in the form of a mineral wool material, especially obtained as a side or waste product from mineral wool production, as indicated above. A material can then be chosen which has the optimal or desired composition for the preparation of the dispersions according to the invention. Such waste materials are formed in large quantities, typically in amounts up to 20-30 % by weight of the starting raw material, in the form of spinning waste, shots and unused fibres of rejected fibrous products (pre-consumer products). One applicable source for the material are also different constructions which are taken down and in which mineral wool material has been used, for instance, as heat insulation (post- consumer products). Such a waste material is already in finely divided, typically fibrous form and can thus be used as such, or alternatively it can also be divided to an even finer form to provide a product with a large surface area, such as 0.4 m²/g or larger, such as up to 25 m²/g, and thus has good dissolution properties in the aqueous solution. Fibres obtained from mineral wool production typically have a diameter of 0.5 to 20, usually 2 to 15 μm, such as 3 to 5 μm as measured with OM or SEM using a suitable method (e.g. Koenig et al, Analytica Chimica Acta 1993 28Q 289-298; Christensen et al, AM IND HYG ASSOC (54) May 1993), and a length of 0.5 to 50, usually 2 to 20 mm, such as 3 to 10 mm.

The aqueous solution is an acidic solution, such as an aqueous solution made acidic by adding an inorganic or organic acid, such as HC1, HNO₃, H₂SO₄, H₃PO₄, formic, acetic, propionic acid or any other suitable mineral or organic acid. The pH of the solution is adjusted suitably. A low pH value results in a rapid dissolution of the mineral material to form a gel, the gelling time being dependent on the pH, a lower pH resulting in a more rapid gelling than a higher pH. Good dissolution for a wide range of mineral materials is obtained at a pH of 0 to 6. The strength of the acid can be, depending on the acid, from 0.1 to 10 M, such as 0.5 to 5 M.

The aqueous solution can also be an alkaline solution, such as an alkali metal or earth alkali metal hydroxy, carbonate or hydrocarbonate solution, especially a sodium, potassium or lithium hydroxide solution, or an ammonium hydroxide solution. Such a solution is preferably 0.1 to 2 molar with respect to the alkaline agent, or has a pH of 10 to 14, in order to easily dissolve also such mineral raw materials which are poorly soluble in neutral solutions.

At an alkaline pH the dispersion tends to be stable and an increase in particle size can be seen. By maintaining the dispersion at an alkaline pH for a suitable time, or by increasing the pH from appr. neutral to pH 10, an increase in particle size is obtained, the increase being less pronounced if the solution in addition contains salts. In the presence of sufficient quantities of salts, such as inorganic salts, e.g. sodium chloride, the particles tend to aggregate to form gels, which precipitate. The same gel formation will also take place by providing an acid pH to the solution, whereby a pH of appr. 2 to below 7 is suitable for gel formation.

Thus by adjusting the pH the dispersion state can be maintained, or the dispersion can be made to gel. The gel can be dispersed and stabilized by using high-shear mixing and raising the pH, and then again be brought to gelling by readjusting (lowering) the pH, or by the addition of an electrolyte.

Alumina containing particulate mineral materials, especially such containing from appr. 10 to 25 % by weight of alumina, are generally relatively poorly soluble in neutral solutions, but exhibit improved dissolution in acidic and alkaline media, thus providing aqueous dispersions containing dissolved silica and dissolved alumina in the desired ratio. According to the invention, when dissolving the material in an acidic solution, organic acids are preferred to inorganic acids. This is due to the fact that inorganic acids can form insoluble salt precipitations, for example with calcium and magnesium included in the starting material. Also some of the inorganic acids are highly corrosive and thus not preferred for obvious reason.

According to a preferred embodiment, the dissolution of the raw material is preferably carried out at an increased temperature, such as at a temperature of 80 to 100°C, preferably while simultaneously stirring, in order to facilitate the dissolution process. Dissolution takes place within a period from 1-2 hours up to 20 hours depending on the dissolving medium used and the solids content of the solution.

Preferably an amount of starting mineral material is dissolved in the solution to provide a metal oxide containing solution which advantageously contains over 1 % by weight, preferably 5 to 60 % by weight of dry matter, which is a suitable concentration for the subsequent use as the binder. After the dissolution is complete, the material nucleates to form a dispersion with the desired particle size. The subsequent stabilization of the dispersion is brought about by creating in the solution electrostatic repulsion between the particles. The electrostatic repulsion between the particles can be effected for example by providing suitable ions in the solution, or by changing the pH of the solution. If necessary, additional water can be added or removed, e.g. by evaporation, if necessary, for example for adjusting the viscosity of the solution obtained.

Stabilization may also be achieved by using suitable surfactants and/or polymers, especially non-ionic ones. Non-ionic surfactants and polymers can be preferred in some cases as they are not very sensitive to an environment which contains high concentra- tions of electrolytes and other chemicals, especially when the ionic strength is high. Examples of suitable polymers are polyethylene oxide and polyethylene glycol. Examples of suitable surfactants are nonylphenols, Tween and Span. In a typical situation, such surfactants and polymers are used in an amount of 0.5 to 2.5 % by weight, calculated from the total solids of the solution. As stated above, the particle size of the dispersion can be adjusted by adjusting the pH.

According to the invention it is thus possible to provide binder dispersions containing predominantly silica in combination with other metal oxides stemming from the starting mineral material, such as calcium oxide, magnesium oxide, aluminium oxide, and possibly further metal oxides in smaller amounts. It is also possible to adjust the reaction conditions so as to obtain dispersions with a desired particle size. The dispersions so obtained can be made to gel either directly after formation, or only immediately prior to application, for example prior to application of the dispersion as a binder onto the mineral raw material. The dispersion can also be made to gel when heating or evaporating water when the final product is shaped.

The composition of the particulate mineral material to be used as raw material for making the briquettes naturally varies depending on the intended use of the briquettes. When the briquettes are to be used for mineral wool production, the particulate mineral material is chosen according to the desired chemical composition of the fibres to be produced. Suitable materials include any of the stone and other mineral materials nor- mally used for this purpose, such as quartz sand, olivine sand, glass, basalt stone, slags, waste material from mineral wool production, lime stone, dolomite, wollastonite, etc. The briquettes are made by simply mixing the mineral material with the binder dispersion, and if necessary, adding water to form a mixture of suitable stiffness. This mixture or mass can be formed into briquettes by compression or compression vibration into briquettes, using per se known techniques, and hardened in connection with the manufacturing process, or later. The hardening process can be accelerated for example by heating. It is also possible to control the hardening time of the briquettes by appropriate selection of pH for the binder solution, thus making it possible for example to manufacture briquettes by extrusion moulding for example.

According to one embodiment of the invention surplus or waste material from mineral wool production are re-used for the manufacture of raw material briquettes for mineral wool production, forming both the mineral raw material as well as the starting material for the binder. The inclusion of such briquettes in the raw material charge does not require any adjustment of the raw material charge.

In the manufacture of mineral wool, the charge can be formed exclusively of briquettes, or the briquettes according to the invention can form a suitable portion of the charge, for use together with further suitable raw materials, which are chosen depending on the composition desired in the final product.

The amount of dispersion to be used as binder can easily be determined by a person skilled in the art. As an example it can be mentioned that when used as a binder in briquettes for mineral wool production, the amount of binder generally is appr. 1 - 15 % by weight, calculated as dry substance, of the dry weight of the product, but it is naturally possible to use higher and lower amounts depending on the desired product and the reactivity of the binder. When used as a binder in metal ore briquettes, a typical amount would be appr. 1 to 15, such as 1 to 5 % by weight of the total weight of the batch.

According to the invention, briquettes with good strength properties, including good green strength properties are obtained. EXAMPLE

Briquettes for mineral wool manufacture can be produced in the following way. 2.1 g of fibres having a composition of 42.1 % SiO₂, 17.4 % Al₂O₃, 17.3 % CaO 13.7 % MgO, 5.8 % FeO, 1.6 % Na₂O, 0.6 % K₂O, the balance being impurities, is dissolved in 100 ml of 1 M formic acid. After dissolution of the fibres, nucleation and stabilization of the solution can be effected by raising the pH close to neutral by adding a suitable alkaline agent, such as sodium hydroxide. Water is evaporated to give a solids content e.g. of 5 % for the dispersion.

An amount of the dispersion so obtained is mixed with the dry components forming the raw material for the briquette, whereby a typical composition for the raw material can be glass waste, basalt and sand, in a ratio of 25: 15:60. The dispersion is added in an amount so that the dry matter of the binder corresponds to 10 % by weight of the total batch. If necessary, additional water can be added to give a stiff mixture. The mass is then formed by compressing or compression vibration into briquettes of a suitable size, a typical volume being appr. 0.5 to 1.0 dm³.

Claims

1. Briquette containing a particulate mineral material and a binder for the mineral material, characterized in that the binder comprises an amorphous silicate based gel binder containing silica and alumina in a molar ratio in the range of 2 - 12.

2. The briquette according to claim 1, wherein the molar ratio between silica and alumina in the binder is in the range of 2.5 - 8.

3. The briquette according to claim 1, wherein the molar ratio between silica and alumina in the binder is in the range of 3.5 - 6.

4. The briquette according to any one of the claims 1 to 3, wherein the silicate binder contains alkali oxide or alkali oxides and the molar ratio between silica and the sum of alkali oxides in the binder is in the range of 10 - 350.

5. The briquette according to claim 4, wherein the molar ratio between silica and the sum of alkali oxides in the binder is in the range of 15 - 150.

6. The briquette according to any one of the preceding claims, wherein the silicate binder contains calcium and/or magnesium oxide and/or iron oxide and the molar ratio between the silica and the sum of calcium oxide, magnesium oxide and iron oxide (as FeO) is in the range of 0.2 - 2, preferably 0.6 - 1.5.

7. The briquette according to any one of the preceding claims, wherein the silicate based binder is derived from a colloidal aqueous dispersion of a mineral material containing silica and alumina in a molar ratio in the range of 2 - 12.

8. The briquette according to any one of the preceding claims, wherein the content of the binder, calculated as dry matter, is 1 to 15 % by weight of the briquette.

9. The briquette according to any one of the preceding claims, wherein the particulate mineral material is a raw material for mineral wool production.

10. The briquette according to claim 9, wherein the particulate mineral material includes re-circulated mineral material, such as residual material from mineral wool production, post-consumer products, flotation waste and glass waste.

11. The briquette according to claim 1 wherein the binder is obtainable by dissolving a particulate mineral material containing silica and alumina in a molar ratio in the range of 2 - 12 in an aqueous solution to form a solution containing nucleated re-precipitated particles of the material, stabilizing the so obtained solution to form a colloidal dispersion having the desired particle size, optionally adjusting the dry matter content of the dispersion, and coagulating the dispersion to form a gel, which is dried.

12. Method for the manufacture of a briquette containing a particulate mineral material and a binder, the method comprising the steps of - providing a particulate mineral material,

- mixing the mineral material with the binder, and water, if necessary,

- shaping the so formed mixture into briquettes, and

- hardening the so formed briquettes, characterized in using a binder comprising an aqueous colloidal silicate dispersion containing silica and alumina in a molar ratio in the range of 2 - 12.

13. The method according to claim 12, wherein the colloidal silicate dispersion is made by dissolving a particulate mineral material containing silica and alumina in a molar ratio of 2 - 12 in an aqueous solution, to form a solution containing nucleated re- precipitated particles from the material, stabilizing the so obtained solution to form a dispersion, and optionally adjusting the dry matter content of the dispersion.

14. The method according to claim 12 or 13, wherein the molar ratio between silica and alumina is in the range of 2.5 - 8, preferably 3.5 - 6.

15. The method according to claim 12, 13 or 14, wherein the silicate dispersion contains alkali oxide or alkali oxides and the molar ratio of silica to the sum of the alkali oxides is in the range of 10 - 350, preferably 15 - 150.

16. The method according to any one of the claims 12 to 15, wherein the colloidal dispersion contains calcium and/or magnesium oxide and/or iron oxide and the molar ratio between the silica and the sum of calcium oxide, magnesium oxide and iron oxide (as FeO) is in the range of 0.2 - 2, preferably 0.6 - 1.5.

17. The method according to any one of the preceding claims 12 to 16, wherein the binder dispersion is adjusted to a dry matter content of 5 to 60 % by weight.

18. The method according to any one of the preceding claims 12 to 17, wherein the dispersion is used in the form of a gel, or is made to gel immediately prior to mixing with the particulate mineral material.

19. The method according to any of the preceding claims 12 to 17, wherein the binder dispersion is made to gel after briquette formation.

20. A process for mineral wool production, whereby mineral raw material in the form of briquettes containing a particulate mineral material and a binder, is added to a melting furnace, the formed melt is withdrawn and fiberized, characterized in that the binder comprises an amorphous silicate based gel binder containing silica and alumina in a molar ratio in the range of 2 - 12.